lsfd: allow filter (--filter/-Q) as extra arguments on command line

[mjt0k]

Currently, any extra arguments on command line gets rejected (lsfd will exit with error). It'd be very useful if lsfd accepted the rest of command line as filter. With this in mind, it would be possible to use, say, tab completion for file names, - since right now it is not possible within the expression to -Q option. Consider:

lsfd -Q 'NAME == "/file/name"'

vs

lsfd NAME == /file/name

The latter seems to be much more user-friendly to me. It is also easier to parse internally.